Microwave heating apparatus

ABSTRACT

A microwave heating apparatus for line heating a dielectric sheet material comprises a trough waveguide having a central ridge extending along the trough, and a metal member spaced from the ridge so that the sheet may be passed in the longitudinal direction of the ridge and between the ridge and the metal member. The dielectric sheet material may be a paper carrying an ink mark to be dried, and the metal member may be a metal drum having the paper extending around it. The trough waveguide extends circumferentially around a portion of the drum and closely follows the drum contour.

United States Patent 1191 Vankoughnett June 19, 1973 [54] MICROWAVE HEATING APPARATUS 3,015,100 12/1961 Rotman 343/772 3,532,848 101970 L t 1. 21910.61 1751 Inventor: Alla P- Vankwghne! Ottawa 2,868,939 1/1959 219/10.55 Ontarw, Canada 3,470,343 9 1969 Bilbrough 219/10.55 x

[73] Assignee: Canadian Patents and Development I Limited, Ottawa, Ontario, Canada 'y Exammer]- Tl'llhe Assistant Examiner-Hugh D. Jaeger 1221 Ffled: July 1971 Attorney-James R. Hughes [21] App]. No.: 160,416

7 [57] ABSTRACT [30] Foreign Application Priority Data A microwave heating apparatus for line heating a di- Nov 27 1970 Canada 099304 electric material wmPriseS a rough Waveguide having a central ridge extending along the trough, and 521 u.s. c1. 219/10.55 343 772 a metal member Spaced fmm idge that the Sheet 51 Int. Cl. 1105b 9/06 may be Passed the longitudinal direction of the ridge [58] Field 61 Search 219/10.55 10.61- and between the ridge and the metal member- The I 343/772 electric sheet material may be a paper carrying an ink mark to be dried, and the metal member may be a [56] References Cited metal drum having the paper extending around it. The trough waveguide extends circumferentially around a UNITED STATES PATENTS portion of the drum and closely follows the drum con- 2,943,325 6/1960 Rotman 343 772 x tout 2,957,173 10/1960 Rotman 343/772 3,013,267 12/1961 Rotman 343/772 1 Claim, 8 Drawing Figures Patented June 19, 1973 .2 Sheefs-Sheet 1 1 MICROWAVE HEATING APPARATUS This invention relates to microwave heating apparatus.

It is often necessary to heat a linear portion of a dielectric sheet material to, for example, dry a marking or glue line on the sheet material.

It has already been proposed to dry a glue line extending along an edge of printed forms by microwave energy, and this has greatly increased the rate at which the drying is accomplished. The apparatus used for drying the glue line has been a slotted waveguide, and the printed forms are passed along the waveguide with the glue line of the forms in the slot so that a field intensification at the slot causes the glue line to dried.

It is possible to heat a line along a sheet material by other dielectric heating apparatus. However, it is difficult to, for example, dry a marking or glue line on adielectric sheet material which is backed by an electrically conducting surface.

One object of the invention is to provide an apparatus for heating by microwave energy a linear portion of a dielectric sheet material which is backed by an electrically conducting metallic surface. The dielectric sheet material may, for example, rest upon or pass over a metal member providing the metallic surface.

Most known microwave heating equipment for heating thin sheets or a linear portion thereof do so by establishing an electric field concentration parallel to the sheet. This method makes most efficient use of the available microwave power; When the sheet is backed by a metallic surface, it is impossible to establish a field which has the electric vector parallel to the surface. Hence, in this case it would only be possible for a microwave heater to operate with a field perpendicular to the metallic surface and the fact that it is only possible to establish this perpendicular field would make it more difficult to efficiently couple energy to the sheet mate rial.

A further object is to provide a microwave heating apparatus for line heating dielectric sheet material backed by a metallic surface, which makes efficient use of the available microwave energy.

One preferred form of the microwave heating apparatus of the invention is for drying an ink line on a sheet of paper backed by a metallic surface. With the apparatus of the invention it is possible to heat by microwave energy a very narrow line, in fact it is possible to heat narrower lines by this apparatus than any other apparatus known to the inventor.

Whilst the above mentioned apparatus for drying a glueline has proved very useful it has a limitation in that a glue line cannot be dried which lies further from the edge of the form than the largest edge portion of the form that can be received by the waveguide through the slot.

It is yet another object of the invention to provide a microwave heating apparatus which is not restricted to heating a marginal edge portion of a dielectric sheet.

Problems that arise in providing a microwave heating apparatus which is not restricted to heating a portion of a dielectric sheet lying within a marginal edge portion of the sheet are that it is difficult to make efficient use of the microwave power supplied to the waveguide and also to reduce as much as possible any hazard to operating personnel from radiant microwave energy.

It is a further object of the invention to provide a microwave heating apparatus that is not restricted to heating a marginal edge portion of the sheet, yet makes efficient use of the microwave power supplied to the waveguide, and wherein any hazard to operating personnel from radiant microwave energy is low.

Other objects of the invention will be apparent from the following description.

According to the invention there is provided a microwave heating apparatus comprising an open trough waveguide having side walls and a base, a ridge attached to a central region of the base between the side walls and extending longitudianally of the waveguide, the height of the ridge being substantially the same as the height of the side walls, and a metal member extending along and covering the open side of the trough, said metal member forming a guide for passing one side of a dielectric sheet adjacent the ridge with the metal member on the other side of the sheet, so that energisation of the waveguide will heat the sheet passed through a region of field intensification between the ridge and the metal member.

In the accompanying drawings which illustrate, by way of example, embodiments of the invention,

FIG. 1 is a partly sectioned side view of a microwave heating apparatus for drying an ink mark,

FIG. 2 is a sectioned end view along II II FIG. 1,

FIG. 3 is a circuit diagram for a non-resonant system of operation.

FIG. 4 is a circuit diagram for a resonant system of operation.

FIG. 5 is a side view of a different microwave heating apparatus for drying an ink mark,

FIG. 6 is an end view in the direction of arrow VI FIG. 5,

FIG. 7 is a sectional end view along VII VII, FIG. 5, and

FIG. 8 is a side view of another microwave heating apparatus for drying a glue line.

In FIG. 1 and 2 there is shown an open trough waveguide generally designated I, having side walls 2 and 4 and a base 6. A ridge 8 is attached to a central region of the base 6 and extends longitudinally of the waveguide 1. The height of the ridge 8 is substantially the same as the height of the side walls 2 and 4.

A metal member in the form of a metal plate 10 is provided for passing one side of a dielectric sheet, in this instance a paper sheet 12 (shown chain-dotted), adjacent the ridge 8 with a metal surface of the metal plate 10 on the other side of the sheet 12.

The waveguide l is supported in spaced relationship from the metal plate 10 by brackets l4, l6 and 18 to which the base 6 is connected. The side walls 2 and 4 have slots 20 and 22 extending along their lengths to provide chokes, as will be described later. The ends of the waveguide l are closed by end plates 24 and 26 provided with coaxial cable connectors 28 and 30 for coaxial cables 32 and 34. The ridge 8 is tapered at 36 and 38 to decrease in height towards each end to provide ridge end transition portions. The ends 40 and 42 of the metal plate 10 are bevelled.

The paper sheet 12 is fed from a supply reel 44 to a take-up reel 46, and passes between the waveguide I and the metal plate 10. An ink marker 48 applies an ink mark (not shown) to the portion of the paper sheet 12 about to pass underneath the ridge 8.

In operation the apparatus is arranged as shown in FIGS. 1 and 2 and set in operation. The ink marker applies an ink mark to the paper sheet 12 from the supply reel 44. The paper sheet 12 with the ink mark on it moves beneath the ridge 8 whilst sliding along the metal plate 10. Microwave energy is propagated along the waveguide from the cable 34 to the cable 32, and as shown in FIG. 2 the ridge 8 alters the field distribution to provide a field concentration extending as is shown by the arrows in FIG. 2 from the ridge 8 through the ink mark on the paper. The ink line is heated and dried by the field established in it.

Although the waveguide 1 is essentially nonradiating, some microwave leakage may occur through the gaps between the side walls 2 and 4 and the metal plate 10. As a precaution against any leakage the slots 20 and 22 may be provided to form chokes.

FIG. 3 shows a non-resonant power supply system for energising the waveguide l. A power supply 48 pro-- vides a dc. voltage to drive a microwave tube, in this instance a magnetron 50. The magnetron 50 generates microwave power which. is delivered by the coaxial cable 34 to the waveguide 1. The coaxial cable 32 delivers unused microwave power to a termination 52 where it is absorbed.

FIG. 4 shows a different, resonant power supply system for energising the waveguide 1. In this embodiment a power supply 54 provides a dc. voltage to drive a magnetron 56.'The.magnetron 56 generates microwave power which is delivered by a coaxial cable 58 to a tuner 60. The tuner 60 is adjusted to force allavailable microwave power from the magnetron 56 to be dissipated in the waveguide 1. The microwave power is delivered by. a'coaxial cable 62 to the waveguide 1 which has a short circuit termination 64 connected to its far end.

In FIGS. to 7 a waveguide 66 extends around a lower portion of a metal member in the form of a drum 68, and an ink marker 70 is shown mounted above the drum 68. The drum 68 rotatably mounted on a shaft 72. The waveguide 66 is slidably mounted on slides 74 and 76 and is movable across the drum by means of an electric motor 78 and lead screw 80.

As shown. in FIG. 7 the waveguide comprises a base 82 and side walls 84 and 86. A ridge 88is attached to a central region of the base 82. Low loss dielectric slabs V .FIGS. 1 and 2.

The ink marker is slidably mounted on slides 98 and 100 and is movable across the drum by an electric motor 10 1 and a lead screw 102. The electric motors 78 and 101 are synchronised to move the waveguide 66 and ink marker 70 across the drum 68 together.

In operation the drum 68, with a paper strip 104 (shown chain-dotted) fitted to it, is rotated so that the ink marker 70 applies an ink line to the paper-strip 104 -at one position across the paper per revolution of the drum 68. The waveguide is energised in, for example, the manner shown in either of FIGS. 3 and 4 and the ridge 88 causes a field concentration to heat and dry the ink line put on the paper strip 104 by the ink marker 70.

The electric field distribution in the heating chamber is illustrated by the arrows shown in FIG. 7. An intense electric field fringes from the central ridge to provide a heating pattern narrowly confined to the ink mark.

As in the previous embodiment the grooves 94 and 96 form chokes to prevent leakage of energy. The slabs 90 and 92 also prevent leakage and improve the concentration of the field at the ridge 88.

It will be appreciated that the ink marker is moved across the paper strip 104 by motor 101, and that the motor 78 is synchronised to move the waveguide ridge 88 to the same position when the marked portion of the paper strip 104 has moved round adjacent the ridge 88.

In FIG. 8 there is shown a waveguide 106 of the same cross-section as that shown in FIGS. 5 to 7 except that the base 108 bowes in the opposite direction. A metal member in the form ofa metal plate 110 extends along the waveguide 106 and two rollers 112 and 114 hold a paper strip 116 (shown chain-dotted) against the waveguide 106. The roller 114 is an applicator roller for applying a marker line-to the paper strip 116 from roller 118 in link tank 120.

In operation the paper strip 116 is continuously moved from the roller 114 to the roller 112 and as in the previous embodiments the waveguide 106 is energised to heat and dry the ink mark applied to the paper strip by the roller 114.

I claim:

1. Microwave heating apparatus, comprising an open trough waveguide having side walls and a base, a ridge attached to a central region of the base between the side walls and extending longitudinally of the waveguide, the height of the ridge being substantially the same as the height of the side walls, and a metal member extending along and covering the whole length of the open side of the trough but spaced from the trough, said metal member forming a guide for passing one side of dielectric sheet adjacent the ridge with the metal member on the other side of the sheet, so that energisation of the waveguide will heat the sheet passed between the ridge and the metal member. 

1. Microwave heating apparatus, comprising an open trough waveguide having side walls and a base, a ridge attached to a central region of the base between the side walls and extending longitudinally of the waveguide, the height of the ridge being substantially the same as the height of the side walls, and a metal member extending along and covering the whole length of the open side of the trough but spaced from the trough, said metal member forming a guide for passing one side of dielectric sheet adjacent the ridge with the metal member on the other side of the sheet, so that energisation of the waveguide will heat the sheet passed between the ridge and the metal member. 